A System of Instruction in the Practical Use of the Blowpipe - Being A Graduated Course Of Analysis For The Use Of Students And All Those Engaged In The Examination Of Metallic Combinations by Anonymous
page 75 of 359 (20%)
page 75 of 359 (20%)
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If the color of the bead is the object desired, the quantity of the substance employed must be very small, else the bead will be so deeply colored, as in some cases to appear almost opaque, as, for instance, in that of cobalt. Should this be the case, then, while the bead is still red hot, it should be pressed flat with the forceps; or it may, while soft, be pulled out to a thin thread, whereby the color can be distinctly discovered. Some bodies, when heated in the borax bead, present a clear bead both while hot and cold; but if the bead be heated with the intermittent flame, or in the flame of reduction, it becomes opalescent, opaque or milk-white. The alkaline earths are instances of this kind of reaction, also glucina oxide of cerium, tantalic and titanic acids, yttria and zirconia. But if a small portion of silica should be present, then the bead becomes clear. This is likewise the case with some silicates, provided there be not too large a quantity present, that is: over the quantity necessary to saturate the borax, for, in that case, the bead will be opaque when cool. If the bead be heated on charcoal, a small tube or cavity must be scooped out of the charcoal, the bead placed in it, and the flame of reduction played upon it. When the bead is perfectly fused, it is taken up between the platinum forceps and pressed flat, so that the color may be the more readily discerned. This quick cooling also prevents the protoxides, if there be any present, from passing into a higher degree of oxidation. The bead should first be submitted to the oxidation flame, and any reaction carefully observed. Then the bead should be submitted to the |
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